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Barnard b
Barnard b is a Super Earth theorized to exist around Barnard's Star, with a chance of 99%. The planet was discovered using wobbles in star's trajectory over 20 years. Being the second closest solar system to ours, Barnard's Star is a common target for many researchers. History Scientists thought about a possible planetary system since 1960, when Peter van de Kamp suggested the existence of two gas giants orbiting at high distance from the star. However, researchers later ruled out the possibility of such giant planets to exist. Many researchers found inconsistent evidence of a possible planetary system over time. They detected wobbles, but were unable to confirm their origin. A possible planet orbiting Barnard's Star was the focus of many sci-fi novels over time. In November 2018, a group of scientists identified with a probability of 99% that a planet should be orbiting Barnard's star. They further suggested that a second planet should orbit at a higher distance. In the same time, they ruled out the possibility of an Earth-like planet orbiting closer, in the habitable zone. The Star Barnard's Star is a red dwarf, a common model among M - type stars. Its mass is 0.144 (1.166 from other authors) times the mass of the Sun. Its diameter is around 0.196 times the diameter of the Sun (1671 thousand km). Luminosity in visual light i 0.0004 times the luminosity of the Sun. Bolometric luminosity (which includes both visible and invisible light) is 0.0035 of Sun's. A significant population of red dwarfs are variable, eruptive and referred as flare stars. Barnard's Star is known to produce flares, but very rare. Flares of red dwarfs are comparable in intensity with Solar flares. However, because the habitable zone is very close, they can have a devastating effect on surrounding planets. Barnard's Star is thought to be a population II star, far older then the Sun. Some scientists suggest that it was there when the galaxy formed, while others suggested that it was not formed within our own galactic cloud. The star has an unusually high proper motion as seen from Earth's sky. This suggests that the star is orbiting the galaxy on a different orbit from the Sun. Certainly, it was not formed from the same cloud as the Solar System. Its metalicity (abundance of heavier elements then helium) is very low, around 20% of the Sun. This clearly indicates a different origin and composition. Because red dwarfs burn their hydrogen very slow, Barnard's Star will still be luminous far beyond the day when Sun will no longer be around. Barnard's Star has a very low rotation period of 130 days, which gives it a greater stability. Flares are usually produced when short-circuits occur between magnetic fields. A low-spinning star has less powerful magnetic fields and very rare flares. Solar System As for 2019, we know, based on detected wobbles, that Barnard's Star does not host any gas giant close enough to be identified. Hubble images and wobble detection ruled out the possibility of giant planets to exist with an orbital period less then 100 years. Scientists ruled out the possibility of Earth-like planets within the habitable zone (which would be between 7 to 15 million km from the star). As for January 2019, we know with a probability of 99% that a Super Earth (Barnard b) orbits at roughly 60 million km (0.4 AU) and that another planet should be orbiting further away, based on unresolved wobbles. Given the old age, it is thought that solar winds had enough time to erode the atmospheres of rocky planets. Also, inner planets locked in the habitable zone had enough time to either be ejected to further orbits or to fall on the star. It is not known if Barnard's Star hosts a Kuiper Belt Given its age, which is at least 10 billion years (and according to other scientists, even greater), Barnard's Star passed close to other stars many times, removing parts of its Kuiper Belt if it had one. Also, outer planets had a significant chance to be removed from their orbits. Not much is known about the solar wind and solar bubble surrounding Barnard's Star. Red Dwarfs usually have low-intensity solar winds during pauses and powerful winds during flares. Also, because of their low luminosity, solar winds are not accelerated too much, as we see in case of the Sun. We can speculate that the heliosphere extends to roughly 3 to 20 AU, but can further extend to over 100 AU during flares. This gives us a very interesting environment, where cosmic rays can sometimes penetrate deeper towards inner planets. The Star Barnard's Star had been a favorite target for many amateur and professional telescopes. So, we have a lot of data to analyze. The star is not homogenous It has brighter and darker spots, which can be used to determine its rotation period. Barnard's Star is a classic M4 spectral-type star, luminosity class V. Its light spectra shows many common feature with other red dwarfs. As seen from the Earth in different wavelengths, the star appears as follows: *Apparent magnitude (ultraviolet) 12.497 *Apparent magnitude (blue) 11.240 *Apparent magnitude (red) 8.298 *Apparent magnitude (infrared) 6.741 *Apparent magnitude (far infrared) 4.524. As one can see, most of the light is emitted in infrared. Visible light is mostly in the red spectra. The star emits 15 times more red then blue light and almost twice less ultraviolet then blue. It also produces 28 times more infrared then red light. Based on this data, we can conclude that ultraviolet light is so dim, that an ozone layer would not be needed to shield a planet in the habitable zone. Flares are thought to occur once every few decades. During flares, the star's emission of visible light increases dramatically. Massive emissions of UV and X rays are also thought to occur too. Planetary Parameters Little is known about the planet, since it cannot be imaged with any telescope. The few data inferred from detected wobbles only help us to determine its orbit and mass: *Distance (semi-major axis): 60.4 million km (0.404 AU) *Excentricity: 0.32 *Orbital period: 233 days *Mass: 3.23 Earth's *Diameter (assumed similar composition with Earth): 1.366 Earth's (17420 km) *Temperature: -170 C or 105 K (might depend on internal composition). The excentricity is surprising, since aged planets would tend to have more circular orbits. This could be a sign that in it's past, the planet was pulled out of its original orbit, maybe after a collision or after the flyby of a free-floating planet. Over lengthy periods of time, most moons tend to move away from their planets, except if they are tidal locked. A cataclysm can also disrupt moons from their orbits or create new ones from an impact. So, we don't know if the planet has a system of moons at all. In an aged system, we could expect planets to rotate much slower or even be tidal locked. However, a cataclysm can change rotation axis or even alter the rotation period dramatically. So, we don't know how should Barnard b be rotating, but we can speculate that it is a low-spinning planet. Given its slightly big eccentricity, it should not be tidal locked. Most probably, it is spinning slowly, like Mercury, but there is no current way to know for sure. Also, if it spins slowly, its axis should not be too tilted, as we see in cases of Mercury or Venus. Chemistry And Inner Structure As Barnard's Star was formed in a completely different time and place then the Sun, its planets must have a totally different composition. The low metallicity suggests that during their formation they would be relatively impoverished in heavier elements. It is thought that the first stars in the universe were massive and after having undergone fusion to the end of their lives provided the Universe all its chemical elements, with the concentration of the heavier elements increasing after each generation of these early short lived stars. So, despite Barnard's star being so old, the planet should contain all known stable elements, but in a different percentage to the planets of our Solar System. Given the age of Barnard System, radioactive elements had more time to decay. So, there would be smaller amounts of uranium and thorium. Uranium 235 should be found in very small amounts, as it decays faster. On the other hand, long exposure with cosmic rays might be involved in the creation of larger amounts of lithium, beryllium, boron or deuterium. There could also be larger deposits of helium 3, which can be used in fusion reactors. Since the planet is far older, its core might be much colder. The core might not be completely solid, smaller but still liquid, like the cores of Mars or the Moon. However, scientists don't exclude the possibility of tidal heating. But even in that case, little tidal heating would come from the pull of the gravity of the star, as it is quite small and distant. Given the low temperature, the planet might be covered with a thick layer of ice and could host a subsurface ocean like Europa. However, given its age, the ice could be much thicker. In addition, carbon dioxide should be frozen on parts of the surface but still periodically sublimating according to the local conditions. Ammonia could be liquid and even form oceans on the surface. However, other gasses, like methane or nitrogen, should be in gaseous phase. We might find deposits of tholins and other carbohydrates on the surface. The planet has a strong enough gravity to hold an atmosphere. The original atmosphere might have been lost, completely or partially, during the early part of its life, when the star was more active and had many flares. However, meteorites and volcanoes can deliver new volatiles to form an atmosphere again. Terraformed Because of its proximity to the Sun, Barnard b would be one of the first targets as humans leave the Solar System. However, terraforming such a planet would be challenging. The major challenge is the low amount of visible light. Plants need both red and blue light to survive. Inside the Solar System, plants can survive as far as the orbit of Neptune using light from the Sun. The Solar Constant for Earth is 1.98. The lowest solar constant, for each kind of light, is 0.002. For Barnard b, the solar constant has the following values: *Infrared light: 0.357 *Red light: 0.0127 *Blue light: 0.0063. As we can see, plants still receive enough blue light to survive, but their production in agriculture will be very small. The Population Limit for Earth, moved to the orbit of Barnard b and protected with greenhouse gasses, would be 16 million people. Since Barnard b is larger, it could support roughly 30 million inhabitants.